The CRISPR-Cas system does not require the generation of customized proteins to target specific sequences but rather a single Cas enzyme can be programmed by a short guide RNA molecule to recognize a specific DNA target. To utilize the CRISPR-Cas system effectively for genome editing without deleterious effects, compositions and methods are needed for optimization and cell-type/tissue/organ specific delivery of these genome engineering tools.
Classic codon optimization introduces synonymous codon substitutions to better match the exogenous gene's codon usage to the codon usage preference of the host. Codon optimization is routinely successful for prokaryotes and unicellular eukaryotes, but has been historically less successful in multicellular eukaryotes.
Classical codon optimization does not take into account differences in codon usage and tRNA frequencies amongst tissue and cell types. There is a need in the art for tissue specific expression of Cas9 and a Cas9 nucleic acid sequence for enhanced expression within a target tissue.